Blower system and method for controlling the same

ABSTRACT

A blower system, including a permanent magnet motor and a wind wheel. The permanent magnet motor includes a stator assembly, a rotor assembly, and a motor controller. The rotor assembly includes a salient pole rotor including a rotor core and magnets embedded in the rotor core. The motor controller includes a microprocessor, a frequency inverter, and a sensor unit. The sensor unit inputs a phase current or phase currents, a phase voltage, and a DC bus voltage into the microprocessor. The microprocessor outputs a signal to control the frequency inverter which is connected to a winding of the stator assembly. The ratio between an air gap of the motor and the thickness of the magnets ranges from 0.03 to 0.065, and the ratio between the length of a pole arc and the length of the magnets ranges from 0.8 to 1.0.

CROSS-REFERENCE TO RELATED APPLICATIONS

Pursuant to 35 U.S.C. § 119 and the Paris Convention Treaty, thisapplication claims the benefit of Chinese Patent Application No.201210179372.6 filed May 31, 2012, the contents of which, including anyintervening amendments thereto, are incorporated herein by reference.Inquiries from the public to applicants or assignees concerning thisdocument or the related applications should be directed to: MatthiasScholl P.C., Attn.: Dr. Matthias Scholl Esq., 14781 Memorial Drive,Suite 1319, Houston, Tex. 77079.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a blower system and a method for controllingthe same.

2. Description of the Related Art

Variable speed blowers are widely used for heating, ventilation, and aircontrol (HVAC). The impellers of the blower rotate under the drive of avariable speed permanent magnetic motor, and the permanent magneticmotor is driven by an electric control system, that is, a motorcontroller. As shown in a block diagram of a current variable speedblower system of FIG. 1, the system includes an HVAC product controller,a motor controller, a permanent magnetic motor, and a blower. The HVACproduct controller, which is commonly a high level product controlpanel, outputs an input command to control the operation of the wholeproduct. The input command includes different operation modes of themotor, such as a constant torque mode, a constant rotational speed mode,or a constant air volume mode.

The motor controller includes a microprocessor that is used to receivethe input commands and to operate the motor in a torque control mode, ora speed control mode, or in a more advanced mode, for example, airvolume control mode. The motor controller further includes a frequencyinverter and a sensing circuit. The frequency inverter produces a pulsewidth modulation (PWM) wave corresponding to different operation modes,and energizes a three-phase winding of a stator. The microprocessordetects operating current and voltage of the motor and receives feedbackinformation through the sensing circuit, and sends out a specificcontrol command to control the operation of the motor.

Conventional variable speed blowers employ a rotor includingsurface-mounted magnetic tiles. FIG. 2 shows a characteristic curve ofthe torque-speed of a typical variable speed blower. When the rotationalspeed of the motor is increased, the torque is required to increase.Thus, when the rotational speed reaches a maximum value, thecorresponding torque requires a maximum torque. As shown in FIG. 2, inan operating position W1 with the maximum rotational speed S1, the rotorhas the maximum torque T1. For a motor including surface mountedpermanent magnets, the operating position W1 is a critical point wherethe frequency inverter is saturated, because the maximum rotationalspeed requires the maximum torque, which in turn requires a saturatedvoltage.

When designing a motor, the required rated torque and the rotationalspeed are generally considered, as shown in the curve of FIG. 2.However, optimizing the controlling strategies is seldom mentioned toextend the maximum rotational speed and torque of a motor. Furthermore,most of the motors have position sensors, thereby resulting in highmaterial and production costs, and potential circuit failure and systemefficiency reduction.

Currently, a typical motor controller employs a sensorless vectorcontrol mode, and focuses on the current vector control. However, thepatent does not disclose any descriptions about using a control strategycombining the saliency of the salient pole rotor with the high fluxdensity to improve the torque density and lower the production cost; ordescriptions about the switch of a torque current control module or adirect stator flux vector control (SFVC) module according to the motoroperation to improve the efficiency and lower the production cost.

SUMMARY OF THE INVENTION

In view of the above-described problems, it is one objective of theinvention to provide a blower system. In the same rated rotational speedand torque, the blower system can lower the manufacturing cost; optimizethe performance, save the energy consumption.

To achieve the above objective, in accordance with one embodiment of theinvention, there is provided a blower system comprising a permanentmagnet motor and a wind wheel driven by the permanent magnet motor. Thepermanent magnet motor comprises a stator assembly comprising a winding,a rotor assembly, and a motor controller. The rotor assembly comprises asalient pole rotor comprising a rotor core and magnets embedded in therotor core. The motor controller employs a sensorless vector controlmode; the motor controller comprises a microprocessor, a frequencyinverter, a sensor unit, and other related peripheral circuits. Thesensor unit senses a phase current or phase currents, a phase voltage,and a DC bus voltage into the microprocessor. The microprocessor outputsa command signal to control the frequency inverter. The frequencyinverter is connected to the windings of the stator assembly. A uniquerotor design in structure dimensions is critical to produce theamplitude and shape of motor airgap flux density waveform. Specifically,It is requires that a ratio between an air gap of the motor and athickness of the magnets ranges from 0.03 to 0.065, and a ratio betweena length of a pole arc and a length of the magnets ranges from 0.8 to1.0.

In a class of this embodiment, the salient pole rotor comprises a rotorcore and a permanent magnet, the rotor core comprises an annular ringhaving a central axial bore and a plurality of magnetic induction blocksprotruding outwards from an outer side of the annular ring; between twoadjacent magnetic induction blocks is formed a radial recess forreceiving the permanent magnets; and a hook block protrudes from themagnetic induction blocks at both sides of an opening of the radialrecess.

In a class of this embodiment, the section of an outer side surface ofthe magnetic induction blocks is a circular-arc line and the outer sidesurface employs a point with a distance deviating from the center of thecentral axial bore as a center of circle.

In a class of this embodiment, the number of magnetic poles of the rotoris 8, 10, or 12.

Advantages of the blower system are summarized below:

-   -   1) The system employs a structure of salient pole rotor, due to        the saliency of the motor, the ratio between the air gap and the        thickness of the magnets ranges from 0.03 to 0.065; the saliency        L_(q)/L_(d) of the salient pole rotor is 1.3-1.7, the length        ratio between the pole arc and the magnets is 0.8-1.0. Based on        the magnetic flux gathering effect generated by two permanent        magnets having the same poles, the surface air gap flux density        of the salient pole rotor ranges from 0.6 to 0.8 Tesla. By        improving the torque density and improving the flux density        through the salient pole structure or by substituting the        ferrite magnets with the original Nd—Fe—B magnets, the        production costs can be reduced meanwhile the motor performance        is remained.    -   2) The control strategy increases the output torque due to the        contribution of the reluctance torque. Under the flux weakening        control, the torque is employed to increase the torque and the        rotational speed, the operating position of the permanent magnet        motor is initiated from W1 to W2. Correspondingly, the output        torque T is increased from T1 to T2, and the rotational speed S        is increased from S1 to S2. Thus, the motor performance is        improved, in other words, the blower system has low production        cost and is energy-saving.    -   3) The invention employs a sensorless vector control mode, thus,        the production cost is further decreased.

It is another objective of the invention to provide a method forcontrolling a blower system. The method can enlarge the torque and therotational speed, in another word, it can lower the manufacturing cost,optimize the performance, and save the energy consumption.

A first technical scheme of the method for controlling a blower systemis summarized herein below:

A method for controlling a blower system, the system comprising apermanent magnet motor and a wind wheel driven by the permanent magnetmotor; the permanent magnet motor comprising a stator assemblycomprising a winding, a rotor assembly, and a motor controller; therotor assembly being a salient pole rotor comprising a rotor core andmagnets embedded in the rotor core; the motor controller employing asensorless vector control mode, the motor controller comprising amicroprocessor, a frequency inverter, and a sensor unit; the sensor unitinputting a phase current or phase currents, a phase voltage, and a DCbus voltage into the microprocessor, and the microprocessor outputting asignal to control the frequency inverter, the frequency inverter beingconnected to the winding of the stator assembly. A unique rotor designin structural dimensions is critical to produce the sinusoidal waveformof airgap flux density. Specifically, it is requires a ratio between anair gap of the motor and a thickness of the magnets ranging from 0.03 to0.065, and a ratio between a length of a pole arc and a length of themagnets ranging from 0.8 to 1.0. An output torque T_(torque) of thesalient pole permanent magnet motor is dependent on a sum of the mainfield torque K_(f)I_(q) and the torque (L_(d)−L_(q))·I_(d)I_(q); and analgorithm control program of the microprocessor takes advantage ofcontributions of a reluctance torque (L_(d)−L_(q))·I_(d)I_(q) to improvethe output torque T_(torque).

In a class of this embodiment, under a flux weakening control, themicroprocessor employs a torque to increase the output torqueT_(torque), an operating position of the permanent magnet motor isinitiated from W1 to W2, correspondingly, the output torque T_(torque)is increased from T1 to T2, and a rotational speed S is increased fromS1 to S2.

A second technical scheme of a method for controlling a blower system issummarized:

A method for controlling a blower system, the system comprising apermanent magnet motor and a wind wheel driven by the permanent magnetmotor; the permanent magnet motor comprising a stator assemblycomprising a winding, a rotor assembly, and a motor controller; therotor assembly being a salient pole rotor comprising a rotor core andmagnets embedded in the rotor core; the motor controller employing asensorless vector control mode, the motor controller comprising amicroprocessor, a frequency inverter, and a sensor unit; the sensor unitinputting a phase current or phase currents, a phase voltage, and a DCbus voltage into the microprocessor, and the microprocessor outputting asignal to control the frequency inverter, the frequency inverter beingconnected to the winding of the stator assembly; a ratio between an airgap of the motor and a thickness of the magnets ranging from 0.03 to0.065, and a ratio between a length of a pole arc and a length of themagnets ranging from 0.8 to 1.0. The method comprises: providing themicroprocessor with a torque current control module and a direct statorflux vector control (SFVC) module, detecting operating parameters andoperating conditions of the motor by the microprocessor, calculating anddetermining whether the frequency inverter is in a saturated state;controlling the operation of the motor by the torque current controlmodule if the frequency inverter is not saturated; or controlling theoperation of the motor by the direct SFVC module if the frequencyinverter is saturated.

In a class of this embodiment, the torque current control module worksin an operating mode of a maximum torque per ampere (MTPA).

In a class of this embodiment, the direct SFVC module works in anoperating mode of a maximum torque per volt (MTPV).

In a class of this embodiment, the microprocessor further comprises astator flux observer by which a flux, a flux angle, and a load angle arecalculated and input into the direct SFVC module.

A third technical scheme of a method for controlling a blower system issummarized:

A method for controlling a blower system, the system comprising apermanent magnet motor and a wind wheel driven by the permanent magnetmotor; the permanent magnet motor comprising a stator assemblycomprising a winding, a rotor assembly, and a motor controller; therotor assembly being a salient pole rotor comprising a rotor core andmagnets embedded in the rotor core; the motor controller employing asensorless vector control mode, the motor controller comprising amicroprocessor, a frequency inverter, and a sensor unit; the sensor unitinputting a phase current or phase currents, a phase voltage, and a DCbus voltage into the microprocessor, and the microprocessor outputting asignal to control the frequency inverter, the frequency inverter beingconnected to the winding of the stator assembly; a ratio between an airgap of the motor and a thickness of the magnets ranging from 0.03 to0.065, and a ratio between a length of a pole arc and a length of themagnets ranging from 0.8 to 1.0; a number of magnetic poles of the rotoris 8, 10, or 12; and the method comprises steps as follows:

-   -   1) determining a critical speed S1 at the moment that the        frequency inverter is saturated, and inputting the critical        speed S1 to the microprocessor;    -   2) providing the microprocessor with a torque current control        module and a direct SFVC module, detecting whether an actual        speed S is higher than the critical speed S1 by the        microprocessor;    -   3) controlling the operation of the motor by the torque current        control module if the actual speed S is no higher than the        critical speed S1; or    -   4) controlling the operation of the motor by the direct SFVC        module if the actual speed S is higher than the critical speed        S1.

A fourth technical scheme of a method for controlling a blower system issummarized:

A method for controlling a blower system, the system comprising apermanent magnet motor and a wind wheel driven by the permanent magnetmotor; the permanent magnet motor comprising a stator assemblycomprising a winding, a rotor assembly, and a motor controller; therotor assembly being a salient pole rotor comprising a rotor core andmagnets embedded in the rotor core; the motor controller employing asensorless vector control mode, the motor controller comprising amicroprocessor, a frequency inverter, and a sensor unit; the sensor unitinputting a phase current or phase currents, a phase voltage, and a DCbus voltage into the microprocessor, and the microprocessor outputting asignal to control the frequency inverter, the frequency inverter beingconnected to the winding of the stator assembly; a ratio between an airgap of the motor and a thickness of the magnets ranging from 0.03 to0.065, and a ratio between a length of a pole arc and a length of themagnets ranging from 0.8 to 1.0; a number of magnetic poles of the rotoris 8, 10, or 12; and the method comprising steps as follows:

-   -   1) determining a critical torque T1 at the moment that the        frequency inverter is saturated, and inputting the critical        torque T1 to the microprocessor;    -   2) providing the microprocessor with a torque current control        module and a direct SFVC module, detecting whether an required        torque T is larger than the critical torque T1 by the        microprocessor;    -   3) controlling the operation of the motor by the torque current        control module if the required torque T is no larger than the        critical torque T1; or    -   4) controlling the operation of the motor by the direct SFVC        module if the required torque T is larger than the critical        torque T1.

A fifth technical scheme of a method for controlling a blower system issummarized:

A method for controlling a blower system, the system comprising apermanent magnet motor and a wind wheel driven by the permanent magnetmotor; the permanent magnet motor comprising a stator assemblycomprising a winding, a rotor assembly, and a motor controller; therotor assembly being a salient pole rotor comprising a rotor core andmagnets embedded in the rotor core; the motor controller employing asensorless vector control mode, the motor controller comprising amicroprocessor, a frequency inverter, and a sensor unit; the sensor unitinputting a phase current or phase currents, a phase voltage, and a DCbus voltage into the microprocessor, and the microprocessor outputting asignal to control the frequency inverter, the frequency inverter beingconnected to the winding of the stator assembly; a ratio between an airgap of the motor and a thickness of the magnets ranging from 0.03 to0.065, and a ratio between a length of a pole arc and a length of themagnets ranging from 0.8 to 1.0; a number of magnetic poles of the rotoris 8, 10, or 12; the microprocessor comprising a torque current controlmodule, a direct SFVC module, and a stator flux observer; and the methodcomprising steps as follows:

-   -   1) reading a required torque;    -   2) determining a d-axis inductance Ld, and a q-axis inductance        Lq in a state of magnetic saturation;    -   3) outputting a stator flux, a flux angle, and a load angle by        the stator flux observer;    -   4) calculating a reference flux based on an operating mode of a        maximum torque per ampere (MTPA);    -   5) calculating a limited flux based on an operating mode of a        maximum torque per volt (MTPV);    -   6) determining whether the limited flux is larger than the        reference flux;    -   7) calculating the voltage Vq according to the requirement of        the torque, and calculating the voltage V_(d) in the operating        mode of MTPA, if the limited flux is larger than the reference        flux, and the frequency inverter is not saturated; or        calculating the voltage V_(q) according to the requirement of        the torque, and calculating the voltage V_(d) in the operating        mode of MTPV, if the limited flux is no larger than the        reference flux;    -   8) converting voltages V_(d) and V_(q) into voltages V_(α) and        V_(β) in a stationary coordinate, converting the voltages V_(α)        and V_(β) in the stationary coordinate into three-phase voltages        V_(a), V_(b), and V_(c), and processing a PWM modulation using        the three-phase voltages V_(a), V_(b), and V_(c).

Advantages of the method for controlling a blower system are summarizedbelow:

-   -   1) The microprocessor of the motor detects operating parameters        and operating conditions of the motor, calculates and determines        whether the frequency inverter is in a saturated state; the        operation of the motor is controlled by the torque current        control module if the frequency inverter is not saturated, or        controlled by the direct SFVC module if the frequency inverter        is saturated; thus, the optimized controlling strategies are        realized, the method improves the torque and the rotational        speed, in another word, the method lowers the manufacturing        costs and saves the energy consumption.    -   2) the torque current control module works in an operating mode        of a maximum torque per ampere MTPA, and the direct SFVC module        works in an operating mode of a maximum torque per volt MTPV;        thus, the method further lowers the energy consumption, and        optimizes the control.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is described herein below with reference to theaccompanying drawings, in which:

FIG. 1 is a block diagram of a blower system;

FIG. 2 is a torque-rotational speed curve of a convention blower system;

FIG. 3 is a schematic diagram of a magnet motor of a blower system inaccordance with one embodiment of the invention;

FIG. 4 is a block diagram of a motor controller of a magnet motor of ablower system in accordance with one embodiment of the invention;

FIG. 5 is a schematic diagram of a salient pole rotor of a permanentmagnet motor of a blower system in accordance with one embodiment of theinvention;

FIG. 6 is a torque-rotational speed curve of a blower system inaccordance with one embodiment of the invention;

FIG. 7 is a control flow chart of a microprocessor of a motor controllerof a blower system in accordance with one embodiment of the invention;

FIG. 8a is a first part of a control flow chart of a blower system inaccordance with one embodiment of the invention;

FIG. 8b is a second part of a control flow chart of a blower system inaccordance with one embodiment of the invention;

FIG. 9 is a coordinate system of a direct SFVC;

FIG. 10 is a block diagram of a direct SFVC having a direct torqueinput;

FIG. 11 is a block diagram of a direct SFVC having a speed input;

FIG. 12 is an expanded view of a direct SFVC module of FIG. 10;

FIG. 13 is an expanded view of a stator flux observer of FIG. 10;

FIG. 14 is a flow chart of a direct stator flux vector controlling theproduction of a reference flux;

FIG. 15 is a flow chart of a direct stator flux vector controlling theproduction of a q-axis maximum current;

FIG. 16 is a diagram of a vector control method in accordance with oneembodiment of the invention; and

FIG. 17 is a size diagram of a salient pole rotor of a permanent magnetmotor in accordance with one embodiment of the invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Detailed description of the invention will be given below in conjunctionwith accompanying drawings.

EXAMPLE 1

A blower system comprises a permanent magnet motor and a wind wheeldriven by the permanent magnet motor. The permanent magnet motor, asshown in FIGS. 3-5, comprises a stator assembly, a rotor assembly 2, anda motor controller. The rotor assembly comprises a rotor core 1 and acoil winding; the rotor core 1 comprises teeth 12 and slots 11, and thecoil winding is winded on the teeth 12. The rotor assembly comprises asalient pole rotor. The motor controller employs a sensorless vectorcontrol mode and comprises a microprocessor, a frequency inverter, and asensor unit. The sensor unit inputs a phase current or phase currents, aphase voltage, and a DC bus voltage into the microprocessor, and themicroprocessor outputs a signal to control the frequency inverter whichis connected to the winding of the stator assembly. A saliencyL_(q)/L_(d) of the salient pole rotor is 1.3-1.7, an air gap fluxdensity on a surface of the salient pole rotor is 0.6-0.8 tesla, themicroprocessor outputs signals to control the frequency inverter througha drive circuit, and the frequency inverter is connected to the windingof the stator assembly.

The salient pole rotor 2 comprises a rotor core 21 and a permanentmagnet 22. The rotor core 21 comprises an annular ring 210 comprising acentral axial bore, and a plurality of magnetic induction blocks 211protruding outwards from an outer side of the annular ring 210; betweentwo adjacent magnetic induction blocks 211 is formed a radial recess 212for receiving the permanent magnet 22; and a hook block 213 protrudesfrom the magnetic induction blocks 211 at both sides of an opening ofthe radial recess 212. A section of an outer side surface 214 of themagnetic induction blocks 211 is a circular-arc line; and the outer sidesurface 214 employs a point A with a distance H deviating from a centerO of the central axial bore as a center of circle. As shown in FIG. 17,an outer dashed line 6 represents an inner wall of the stator, an innerdashed line 7 represents an outer edge of the stator core 21, betweenthe outer dashed line 7 and the inner dashed line 6 a gap is formed in aradial direction, which is called an air gap L1. The permanent magnet 22is also called magnets, the thickness of which is labeled as H. A ratiobetween the air gap L1 and a thickness of the magnets H ranges from 0.03to 0.065, which controls the saliency Lq/Ld of the salient pole rotorbetween 1.3 and 1.7. A ratio between a length of a pole arc L2 of thestator core 21 and a length of the magnets ranges L3 from 0.8 to 1.0.Based on the magnetic flux gathering effect generated by two permanentmagnets having the same poles, the surface air gap flux density of thesalient pole rotor ranges from 0.6 to 0.8 Tesla. By improving the torquedensity and improving the flux density via the salient pole structure,or by substituting the ferrite with the original Nd—Fe—B as the magnets,the production cost can be decreased. The number of magnetic poles ofthe rotor is 8, 10, or 12.

For a salient pole permanent magnet motor, the production cost can bedecreased by improving the torque density, or controlling the saliencyof the motor; or the torque can be decreased by employing a specialcontrol strategy.

The output torque of the salient pole permanent magnet motor isdependent on a sum of the main field torque K_(f)I_(q) and the torque(L_(d)−L_(q))·I_(d)I_(q), as shown in the following formula, it is knownthat the torque comprises two parts, one part is produced by thepermanent magnetic field and the current I_(g), the other part isproduced by the reluctance torque, which is dependent on the salientpole inductance, and two current I_(q) and I_(d).T_(torque)=>K_(f)I_(q)+(L_(d)−L_(q))·I_(d)I_(q)

A torque-rotational speed characteristic curve of an inner permanentmagnet motor of a motor system of the invention is shown in FIG. 6. Theconventional strategy is that, the motor runs at a base rotational speedS1 at the operating position W1, the frequency inverter is saturated atthe base rotational speed S1, thus, it cannot provide with anymorecurrent to produce a larger torque. Compared with the conventionalstrategy, the example provides an inner permanent magnet motor having asalient pole rotor; the output torque is increased due to thecontributions of the reluctance torque. Under a flux weakening control,the microprocessor employs a torque to increase the output torqueT_(torque), the operating position of the permanent magnet motor isinitiated from W1 to W2. Correspondingly, the output torque T_(torque)is increased from T1 to T2, and the rotational speed S is increased fromS1 to S2.

The blower system employing the salient pole permanent magnet motor, notonly improves the torque density, but also decreases the production costby controlling the saliency of the motor. Furthermore, by the controlstrategy, the output torque is increased due to the contribution of thereluctance torque. Under the flux weakening control, the lifting torqueis employed to increase the torque and the rotational speed, theoperating position of the permanent magnet motor is initiated from W1 toW2. Correspondingly, the output torque T is increased from T1 to T2, andthe rotational speed S is increased from S1 to S2. Thus, the motorperformance is improved, in another word, the blower system has lowproduction cost and is energy-saving.

EXAMPLE 2

A method for controlling a blower system is shown in FIGS. 4 and 7. Thesystem comprises a permanent magnet motor and a wind wheel driven by thepermanent magnet motor. The permanent magnet motor comprises a statorassembly, a rotor assembly, and a motor controller. The rotor assemblycomprises a salient pole rotor comprising a rotor core and magnetsembedded in the rotor core. The motor controller employs a sensorlessvector control mode and comprises a microprocessor, a frequencyinverter, and a sensor unit, of them, the sensor unit inputs a phasecurrent or phase currents, a phase voltage, and a DC bus voltage intothe microprocessor, and the microprocessor outputs a signal to controlthe frequency inverter; the frequency inverter is connected to a windingof the stator assembly. A ratio between an air gap of the motor and athickness of the magnets ranging from 0.03 to 0.065, and a ratio betweena length of a pole arc and a length of the magnets ranging from 0.8 to1.0. The number of magnetic poles of the rotor is 8, 10, or 12. Themethod comprises:

-   -   providing the microprocessor with a torque current control        module and a direct SFVC module, detecting operating parameters        and operating conditions of the motor by the microprocessor,        calculating and determining whether the frequency inverter is in        a saturated state;    -   controlling the operation of the motor by the torque current        control module if the frequency inverter is not saturated; or    -   controlling the operation of the motor by the direct SFVC module        if the frequency inverter is saturated.

The torque current control module works in an operating mode of amaximum torque per ampere MTPA.

The direct SFVC module works in an operating mode of a maximum torqueper volt MTPV.

The microprocessor further comprises a stator flux observer by which aflux, a flux angle, and a load angle are calculated and input into thedirect SFVC module.

EXAMPLE 3

A method for controlling a blower system is shown in FIGS. 6 and 7. Thesystem comprises a permanent magnet motor and a wind wheel driven by thepermanent magnet motor. The permanent magnet motor comprises a statorassembly, a rotor assembly, and a motor controller. The rotor assemblycomprises a salient pole rotor comprising a rotor core and magnetsembedded in the rotor core. The motor controller employs a sensorlessvector control mode and comprises a microprocessor, a frequencyinverter, and a sensor unit, of them, the sensor unit inputs a phasecurrent or phase currents, a phase voltage, and a DC bus voltage intothe microprocessor, and the microprocessor outputs a signal to controlthe frequency inverter; the frequency inverter is connected to a windingof the stator assembly. A ratio between an air gap of the motor and athickness of the magnets ranging from 0.03 to 0.065, and a ratio betweena length of a pole arc and a length of the magnets ranging from 0.8 to1.0. The number of magnetic poles of the rotor is 8, 10, or 12. Themethod comprises:

-   -   1) determining a critical speed S1 at the moment that the        frequency inverter is saturated, and inputting the critical        speed S1 to the microprocessor;    -   2) providing the microprocessor with a torque current control        module and a direct SFVC module, detecting whether an actual        speed S is higher than the critical speed S1 by the        microprocessor;    -   3) controlling the operation of the motor by the torque current        control module if the actual speed S is no higher than the        critical speed S1; or    -   4) controlling the operation of the motor by the direct SFVC        module if the actual speed S is higher than the critical speed        S1.

EXAMPLE 4

A method for controlling a blower system is shown in FIGS. 6 and 7. Thesystem comprises a permanent magnet motor and a wind wheel driven by thepermanent magnet motor. The permanent magnet motor comprises a statorassembly, a rotor assembly, and a motor controller. The rotor assemblycomprises a salient pole rotor comprising a rotor core and magnetsembedded in the rotor core. The motor controller employs a sensorlessvector control mode and comprises a microprocessor, a frequencyinverter, and a sensor unit, of them, the sensor unit inputs a phasecurrent or phase currents, a phase voltage, and a DC bus voltage intothe microprocessor, and the microprocessor outputs a signal to controlthe frequency inverter; the frequency inverter is connected to a windingof the stator assembly. A ratio between an air gap of the motor and athickness of the magnets ranging from 0.03 to 0.065, and a ratio betweena length of a pole arc and a length of the magnets ranging from 0.8 to1.0. The number of magnetic poles of the rotor is 8, 10, or 12. Themethod comprises:

-   -   1) determining a critical torque T1 at the moment that the        frequency inverter is saturated, and inputting the critical        torque T1 to the microprocessor;    -   2) providing the microprocessor with a torque current control        module and a direct SFVC module, detecting whether an required        torque T is larger than the critical torque T1 by the        microprocessor;    -   3) controlling the operation of the motor by the torque current        control module if the required torque T is no larger than the        critical torque T1; or    -   4) controlling the operation of the motor by the direct SFVC        module if the required torque T is larger than the critical        torque T1.

EXAMPLE 5

A method for controlling a blower system is shown in FIGS. 8a and 8b.The system comprises a permanent magnet motor and a wind wheel driven bythe permanent magnet motor. The permanent magnet motor comprises astator assembly, a rotor assembly, and a motor controller. The rotorassembly comprises a salient pole rotor comprising a rotor core andmagnets embedded in the rotor core. The motor controller employs asensorless vector control mode and comprises a microprocessor, afrequency inverter, and a sensor unit, of them, the sensor unit inputs aphase current or phase currents, a phase voltage, and a DC bus voltageinto the microprocessor, and the microprocessor outputs a signal tocontrol the frequency inverter; the frequency inverter is connected to awinding of the stator assembly. A ratio between an air gap of the motorand a thickness of the magnets ranging from 0.03 to 0.065, and a ratiobetween a length of a pole arc and a length of the magnets ranging from0.8 to 1.0. The number of magnetic poles of the rotor is 8, 10, or 12.The microprocessor comprising a torque current control module, a directSFVC module, and a stator flux observer. The method comprises:

-   -   1) reading a required torque;    -   2) determining an inductance Ld, and an inductance Lq in a state        of magnetic saturation;    -   3) outputting a stator flux, a flux angle, and a load angle by        the stator flux observer;    -   4) calculating a reference flux based on an operating mode of a        maximum torque per ampere (MTPA);    -   5) calculating a limited flux based on an operating mode of a        maximum torque per volt (MTPV);    -   6) determining whether the limited flux is larger than the        reference flux;    -   7) calculating the voltage V_(q) according to the requirement of        the torque, and calculating the voltage V_(d) in the operating        mode of MTPA, if the limited flux is larger than the reference        flux, and the frequency inverter is not saturated; or        calculating the voltage V_(q) according to the requirement of        the torque, and calculating the voltage V_(d) in the operating        mode of MTPV, if the limited flux is no larger than the        reference flux; and    -   8) converting voltages V_(d) and V_(q) into voltages V_(α) and        V_(β) in a stationary coordinate, converting the voltages V_(α)        and V_(β) in the stationary coordinate into three-phase voltages        V_(a), V_(b), and V_(c), and processing a PWM modulation using        the three-phase voltages V_(a), V_(b), and V_(c). The torque        current control module, the direct SFVC module, the operating        mode of the MTPA, and the operating mode of the MTPV are        described herein below:

1) The torque current control module is a commonly used module tocontrol the permanent magnet motor in the motor system. Under a commandof the required rotational speed and torque from the outside, therequired torque is achieved; the torque is converted into the actualoperating current of the motor, and the motor works at the actualoperating current under the closed-looped control. The control mode isvery efficient when the frequency inverter is not saturated.

2) In the vector control for a permanent magnet synchronous motor(PMSM), an optimal control is to acquire a maximum output torque at alowest current; an operating mode of MTPA, compared with other operatingmodes, acquires the same torque at a lowest current, such an operatingmode is very efficient when the frequency inverter is not saturated.However, when the frequency inverter is saturated, the operating mode ofMTPA is not applicable. The operating mode of MTPA is described in manytextbooks, patent literatures, and papers.

The direct SFVC module is as shown in FIG. 9, in which, vector referencecoordinates of the PMSM are defined: stationary coordinatesa, β; rotorcoordinates d, q; and stator coordinates d_(s), q_(s).

In the stationary coordinates α, β, the relation between the voltage andthe torque of the inner PMSM is as follows:

$\begin{matrix}{{\overset{\_}{\nu}}_{\alpha\beta} = {{R_{s} \cdot {\overset{\_}{i}}_{\alpha\beta}} + \frac{d{\overset{\_}{\lambda}}_{a\;\beta}}{dt}}} & (1) \\{T_{e} = {\frac{3}{2} \cdot p \cdot \left( {{\lambda_{\alpha} \cdot i_{\beta}} - {\lambda_{\beta} \cdot i_{\alpha}}} \right)}} & (2)\end{matrix}$

R_(s) represents a stator resistor, and p represents a number of polepairs.

The control mode of the motor is achieved by coupling current throughthe magnetic flux, and the control is converted into an electromagneticflux control. For an inner PMSM, the formula of the rotor coordinates d,q is as follows:

$\begin{matrix}{{\overset{\_}{\lambda}}_{dq} = {{{\lbrack L\rbrack \cdot \begin{bmatrix}i_{d} \\i_{q}\end{bmatrix}} + \begin{bmatrix}\lambda_{m} \\0\end{bmatrix}} = \begin{bmatrix}{\lambda_{d}\left( {i_{d},i_{q}} \right)} \\{\lambda_{q}\left( {i_{d},i_{q}} \right)}\end{bmatrix}}} & (3)\end{matrix}$

λ_(m) represents magnetic flux linkage.

If the flux is not in a saturated state, the above formula (3) can besimplified as:

$\begin{matrix}{{\overset{\_}{\lambda}}_{dq} = {{\begin{bmatrix}L_{d} & 0 \\0 & L_{q}\end{bmatrix} \cdot \begin{bmatrix}i_{d} \\i_{q}\end{bmatrix}} + \begin{bmatrix}\lambda_{m} \\0\end{bmatrix}}} & (4)\end{matrix}$

L_(d) is an inductance of a d-axis of the motor, and L_(q) is aninductance of a q-axis of the motor.

If the rotor's position is ν, and the magnet domain in the coordinatesα, β, the formulaic:

$\begin{matrix}\begin{matrix}{{\overset{\_}{\lambda}}_{\alpha\beta} = {{A\left( {- \vartheta} \right)} \cdot {\overset{\_}{\lambda}}_{dq}}} \\{= {{A\left( {- \vartheta} \right)} \cdot \left\{ {{\begin{bmatrix}L_{d} & 0 \\0 & L_{q}\end{bmatrix} \cdot {{A(\vartheta)}\ \begin{bmatrix}i_{\alpha} \\i_{\beta}\end{bmatrix}}} + \begin{bmatrix}\lambda_{m} \\0\end{bmatrix}} \right\}}} \\{{A(\vartheta)} = \begin{bmatrix}{\cos(\vartheta)} & {\sin(\vartheta)} \\{- {\sin(\vartheta)}} & {\cos(\vartheta)}\end{bmatrix}}\end{matrix} & (5)\end{matrix}$

In the stator coordinates d_(s), q_(s), the voltage-torque relation is:

$\begin{matrix}{{\overset{\_}{\nu}}_{dqs} = {{R_{s} \cdot {\overset{\_}{i}}_{dqs}} + {\frac{d}{dt}\begin{bmatrix}\lambda \\0\end{bmatrix}} + {\lambda \cdot \begin{bmatrix}0 \\{\omega + \frac{d\delta}{dt}}\end{bmatrix}}}} & (6) \\{T_{e} = {{\left( {3/2} \right) \cdot p \cdot \lambda \cdot i_{qs}} = {k_{T} \cdot i_{qs}}}} & (7)\end{matrix}$

ω represents the rotational speed, and δ represents the load angle.

In reference to formula (6), the stator flux vector λ, and voltage ofd-axis are directly modified, whereas the load angle and the torque canbe controlled by the voltage of q-axis; as shown in formula (7), thecurrent of q_(s) axis directly controls the torque.

As shown in FIG. 10, a control combination block diagram of a torquecontrol mode and a flux control comprises a direct flux vector control(DFVC), a stator flux observer, and a dead-time compensation module. Atorque command is input via a torque gain, and the torque command isused as a required torque standard to adjust the torque.

As shown in FIG. 11, a control combination block diagram of a speedcontrol mode and a flux control comprises a DFVC, a stator fluxobserver, and a dead-time compensation module. A speed control commandis used as a standard for a proportional integral controller, and aspeed loop controller produces a torque command.

A block diagram of the DFVC is shown in FIG. 12. The technical scheme iscarried out in a stator flux base structure. The flux observer inputsfeedback information and an output of the flux into a DFVC strategy. Thetorque command controls the reference variables. The DFVC comprises twocontrol loops, that is, a stator flux loop and a q-axis current loop,and a proportional integral controller is used to control the twocontrol loops. The DFVC strategy is advantageous in that, when adjustingthe flux and current, the frequency voltage, limitations of current andload angle are taken into consideration.

FIG. 13 is a block diagram of the stator flux observer, in which, theobserver is a critical part to provide a stator flux value, a positionof stator flux, and a load angle. The output of the stator flux observeris an input of the DFVC. The stator flux observer is a combination oftwo models, and chooses a corresponding control mode to operate based onwhether the frequency controller is saturated or not. When therotational speed is low, the motor runs in the current mode, the controlis accomplished by controlling the current according to the inputtorque, that is, the torque current control module; when the rotationalspeed is high, the motor runs in the voltage mode which only controlsthe voltage, that is, the direct SFVC module. The crossing anglefrequency changes between a low speed and a high speed mode, and can bedefined by the gain (rad/s) of the observer.

FIG. 14 is a block diagram for producing a reference flux module. Underthe controls of a low speed MTPA and a flux weakening of a torque, thereference flux production module provides a reference flux based on asaturated frequency inverter or a range of speed. As shown in FIG. 6,when a basic rotational speed is W1, the reference flux is provided byan optimal operating mode, i.e., the maximum torque per ampere MTPA. Theoperating mode of MTPA is a nonlinear curve, and such a nonlinear curvecan be acquired in a characteristic test, or simulated by a finiteelement analysis. Then, a look-up table method is effectively carriedout. When the rotational speed is increased, the back-electromotiveforce of the motor is increased, and the frequency inverter begins to besaturated, which allows the voltage limitation to work, and at the sametime, the conditions of MTPA do not work anymore. The highest voltage isdependent on the PWM strategy and a transient DC linkage voltage, thevoltage limitation is accomplished by limiting the stator referenceflux, and the reference value is provided by a weak magnet limitingmodule. According to the method, the switch between the flux weakeningcontrol and the MTPA control can be automatically carried out, which isbased on a practical and efficient highest DC bus voltage and therequired q-axis current. As shown in FIG. 10, the action of the voltagelimitation is something like to output magnetic flux to the currentcontroller.

The formula of the voltage limitation is:(R_(s)i_(ds))²+(R_(s)i_(qs)+ωλ)²≤V_(s,max) ²  (8)

V_(s,max) is dependent on the PWM strategy and the transient DC busvoltage V_(dc).

From the formula (8), it is known that the operation of voltagelimitation is to limit the stator flux.

$\begin{matrix}{\begin{matrix}{\lambda_{\lim} = \frac{\left. {\sqrt{V_{smax}^{2} - \left( {R_{s} \cdot i_{sd}} \right)^{2}} - {R_{s} \cdot}} \middle| i_{qs} \right|}{|\omega|}} \\{\cong \frac{\left. {V_{s,\max} - {R_{s} \cdot}} \middle| i_{qs} \right|}{|\omega|}}\end{matrix}{V_{s,\max} = {V_{dc}/\sqrt{3}}}} & (9)\end{matrix}$

As shown in FIG. 15, a block diagram for producing a maximum q-axiscurrent, and limitations of the current and the load angle in the MTPVcontrol strategy of the lifting torque is shown. In order to transmitthe required torque, the q-axis current is calculated from thetorque/current production module in FIG. 10. However, the q-axis currentis limited by the maximum current of the frequency inverter. Therequired current of the q-axis is bidirectionally controlled by thecurrent limiter.

The q-axis current is limited by the maximum current of the frequencyinverter, and the maximum current of the q-axis q_(s) is defined as:

$\begin{matrix}{i_{{qs},\max} \leq \sqrt{I_{s,\max}^{2} - i_{ds}^{2}}} & (10)\end{matrix}$

the i_(ds) is the stator current of the d_(s)-axis.

In process of increasing the torque under high speed, the optimalcontrol strategy is to maximize efficiency of the usable phase voltageto achieve a lowest current. In order to realize the strategy, theconditions for motor operation requiring to open or close the maximumload angle are defined as MTPV operation. The maximum load angle isacquired by the analyses of the load angle, which comprises an imitationand an acceleration test. The determination of the maximum load angleimproves the stability of the motor, which is like the limitation of theload angle. As shown in FIG. 15, the limitation of the load angle isaccomplished by the PI controller, thus the maximum allowable current islowered.

As shown in FIG. 16, in a low speed range, the motor controller is in anoperating mode of MTPA, a section of the curve is labeled as (0, W1),and the current vector is ISW1. As the speed increases, the frequencyinverter becomes saturated, the motor operates in a curve of MTPVoperating mode, that is, the section (W1, W2), and the current vector isW2. Thus, the maximum torque and rotational speed is achieved, and thecontrol mode is efficient and energy saving. The current vector IWn is acurrent transition vector from W1 to W2. As shown in FIG. 16, thesection of the curve is very short, which means, the transition part isvery efficient, and energy-saving.

Descriptions of FIGS. 9-16 are specifically summarized in sometextbooks, and will not be summarized herein.

While particular embodiments of the invention have been shown anddescribed, it will be obvious to those skilled in the art that changesand modifications may be made without departing from the invention inits broader aspects, and therefore, the aim in the appended claims is tocover all such changes and modifications as fall within the true spiritand scope of the invention.

The invention claimed is:
 1. A blower system, comprising: a) a permanentmagnet motor, the permanent magnet motor comprising a stator assemblycomprising a winding, a rotor assembly, and a motor controller; and b) awind wheel driven by the permanent magnet motor; wherein the rotorassembly comprises a salient pole rotor comprising a rotor core andmagnets embedded in the rotor core; the motor controller employs asensorless vector control mode and comprises a microprocessor having adirect stator flux vector control (SFVC) module, a frequency inverter,and a sensor unit; wherein, the direct SFVC module is adapted to adjusta d-axis voltage V_(d) of the motor in a rotor coordinate according toflux in the stator assembly; the sensor unit inputs a phase current orphase currents, a phase voltage, and a DC bus voltage into themicroprocessor, and the microprocessor outputs a signal to control thefrequency inverter; the frequency inverter is connected to the windingof the stator assembly; and a ratio between an air gap of the motor anda thickness of the magnets ranges from 0.03 to 0.065, and a ratiobetween a length of a pole arc and a length of the magnets ranges from0.8 to 1.0.
 2. The blower system of claim 1, wherein the rotor corecomprises an annular ring comprising a central axial bore, and aplurality of magnetic induction blocks protruding outwards from an outerside of the annular ring; between two adjacent magnetic induction blocksis formed a radial recess for receiving permanent magnets; and a hookblock protrudes from the magnetic induction blocks at both sides of anopening of the radial recess.
 3. The blower system of claim 2, wherein asection of an outer side surface of the magnetic induction blocks is acircular-arc line; and the outer side surface employs a point with adistance deviating from the center of the central axial bore as a centerof circle.
 4. The blower system of claim 3, wherein a number of magneticpoles of the rotor is 8, 10, or
 12. 5. A method for controlling a blowersystem, the system comprising a permanent magnet motor and a wind wheeldriven by the permanent magnet motor; the permanent magnet motorcomprising a stator assembly comprising a winding, a rotor assembly, anda motor controller; the rotor assembly being a salient pole rotorcomprising a rotor core and magnets embedded in the rotor core; themotor controller employing a sensorless vector control mode, the motorcontroller comprising a microprocessor, a frequency inverter, and asensor unit; the sensor unit inputting a phase current or phasecurrents, a phase voltage, and a DC bus voltage into the microprocessor,and the microprocessor outputting a signal to control the frequencyinverter, the frequency inverter being connected to the winding of thestator assembly; a ratio between an air gap of the motor and a thicknessof the magnets ranging from 0.03 to 0.065, and a ratio between a lengthof a pole arc and a length of the magnets ranging from 0.8 to 1.0; anumber of magnetic poles of the rotor is 8, 10, or 12; and the methodcomprising: providing the microprocessor with a torque current controlmodule and a direct stator flux vector control (SFVC) module, detectingoperating parameters and operating conditions of the motor by themicroprocessor, calculating and determining whether the frequencyinverter is in a saturated state; wherein, the direct SFVC module isadapted to adjust a d-axis voltage V_(d) of the motor in a rotorcoordinate according to flux in the stator assembly; and controlling theoperation of the motor by the torque current control module if thefrequency inverter is not saturated; or controlling the operation of themotor by the direct SFVC module if the frequency inverter is saturated.6. The method of claim 5, wherein the torque current control moduleworks in an operating mode of a maximum torque per ampere (MTPA).
 7. Themethod of claim 5, wherein the direct SFVC module works in an operatingmode of a maximum torque per volt (MTPV).
 8. The method of claim 5,wherein the microprocessor further comprises a stator flux observer bywhich a flux, a flux angle, and a load angle are calculated and inputinto the direct SFVC module.
 9. A method for controlling a blowersystem, the system comprising a permanent magnet motor and a wind wheeldriven by the permanent magnet motor; the permanent magnet motorcomprising a stator assembly comprising a winding, a rotor assembly, anda motor controller; the rotor assembly being a salient pole rotorcomprising a rotor core and magnets embedded in the rotor core; themotor controller employing a sensorless vector control mode, the motorcontroller comprising a microprocessor, a frequency inverter, and asensor unit; the sensor unit inputting a phase current or phasecurrents, a phase voltage, and a DC bus voltage into the microprocessor,and the microprocessor outputting a signal to control the frequencyinverter, the frequency inverter being connected to the winding of thestator assembly; a ratio between an air gap of the motor and a thicknessof the magnets ranging from 0.03 to 0.065, and a ratio between a lengthof a pole arc and a length of the magnets ranging from 0.8 to 1.0; anumber of magnetic poles of the rotor is 8, 10, or 12; and the methodcomprising steps as follows: 1) determining a critical speed S1 at themoment the frequency inverter is saturated, and inputting the criticalspeed S1 to the microprocessor; 2) providing the microprocessor with atorque current control module and a direct SFVC module, detectingwhether an actual speed S is higher than the critical speed S1 by themicroprocessor; and 3) controlling the operation of the motor by thetorque current control module if the actual speed S is no higher thanthe critical speed S1; or 4) controlling the operation of the motor bythe direct SFVC module if the actual speed S is higher than the criticalspeed S1.
 10. A method for controlling a blower system, the systemcomprising a permanent magnet motor and a wind wheel driven by thepermanent magnet motor; the permanent magnet motor comprising a statorassembly comprising a winding, a rotor assembly, and a motor controller;the rotor assembly being a salient pole rotor comprising a rotor coreand magnets embedded in the rotor core; the motor controller employing asensorless vector control mode, the motor controller comprising amicroprocessor, a frequency inverter, and a sensor unit; the sensor unitinputting a phase current or phase currents, a phase voltage, and a DCbus voltage into the microprocessor, and the microprocessor outputting asignal to control the frequency inverter, the frequency inverter beingconnected to the winding of the stator assembly; a ratio between an airgap of the motor and a thickness of the magnets ranging from 0.03 to0.065, and a ratio between a length of a pole arc and a length of themagnets ranging from 0.8 to 1.0; a number of magnetic poles of the rotoris 8, 10, or 12; and the method comprising steps as follows: 1)determining a critical torque T1 at the moment the frequency inverter issaturated, and inputting the critical torque T1 to the microprocessor;2) providing the microprocessor with a torque current control module anda direct SFVC module, detecting whether an required torque T is largerthan the critical torque T1 by the microprocessor; and 3) controllingthe operation of the motor by the torque current control module if therequired torque T is no larger than the critical torque T1; or 4)controlling the operation of the motor by the direct SFVC module if therequired torque T is larger than the critical torque T1.
 11. A methodfor controlling a blower system, the system comprising a permanentmagnet motor and a wind wheel driven by the permanent magnet motor; thepermanent magnet motor comprising a stator assembly comprising awinding, a rotor assembly, and a motor controller; the rotor assemblybeing a salient pole rotor comprising a rotor core and magnets embeddedin the rotor core; the motor controller employing a sensorless vectorcontrol mode, the motor controller comprising a microprocessor, afrequency inverter, and a sensor unit; the sensor unit inputting a phasecurrent or phase currents, a phase voltage, and a DC bus voltage intothe microprocessor, and the microprocessor outputting a signal tocontrol the frequency inverter, the frequency inverter being connectedto the winding of the stator assembly; a ratio between an air gap of themotor and a thickness of the magnets ranging from 0.03 to 0.065, and aratio between a length of a pole arc and a length of the magnets rangingfrom 0.8 to 1.0; a number of magnetic poles of the rotor is 8, 10, or12; the microprocessor comprising a torque current control module, adirect SFVC module, and a stator flux observer; and the methodcomprising steps as follows: 1) reading a required torque; 2)determining ad-axis a d-axis inductance L_(d), and a q-axis inductanceL_(q) in the state of magnetic saturation; 3) outputting a stator flux,a flux angle, and a load angle by the stator flux observer; 4)calculating a reference flux based on an operating mode of a maximumtorque per ampere (MTPA); 5) calculating a limited flux based on anoperating mode of a maximum torque per volt (MTPV); 6) determiningwhether the limited flux is larger than the reference flux; 7)calculating the voltage V_(q) according to the requirement of thetorque, and calculating the voltage V_(d) in the operating mode of MTPAif the limited flux is larger than the reference flux and the frequencyinverter is not saturated; or calculating the voltage V_(q) according tothe requirement of the torque, and calculating the voltage V_(d) in theoperating mode of MTPV if the limited flux is no larger than thereference flux; and 8) converting the voltages V_(d) and V_(q) intovoltages V_(α) and V_(β) in a stationary coordinate, converting thevoltages V_(α) and V_(β) in the stationary coordinate into three-phasevoltages V_(a), V_(b), and V_(c), and modulating a PWM using thethree-phase voltages V_(a), V_(b), and V_(c).